Casting sodium-lead alloys



Jan. 5, 1954 G. w: BESTE 2,664,605

CASTING SODIUM-LEAD ALLOYS Filed Dec. 6, 1951 l3 l5 l5 FIG. 2

- IN VEN TOR.

GEORGE W. BE 5 TE Patented Jan. 5, 1954 CASTING SODIUM-LEAD ALLOYS George W. Beste, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware Application December 6, 1951, Serial No. 260,178

4 Claims.

This invention relates to the manufacture of sodium-lead alloys. More particularly, the invention relates to a new and improved continuous process for the solidification of such alloys, and the comminution to discrete particles particularly suitable for subsequent ethylation or other chemical processes.

The alloys of sodium and lead find extensive chemical usage in the manufacture of the alkyl compounds of lead, particularly tetraethyllead by the ethylation of the monosodium alloy, NaPb, with ethyl chloride. In the past, such alloys have been manufactured in the following manner. Sodium and lead have been combined in the liquid phase, in large batches, and such molten alloy has then been solidified in large slabs. Such slabs were then comminuted by vibratory shaking and subsequent crushing. Apparatus and process suitable for this prior commercial methd are illustrated by Stecher Patent 2,134,091. Although fully operable, this prior method has certain disadvantages which have heretofore been recognized but not fully overcome. For example, the intermittent high temperature variation to which parts of the Stecher caster are subjected has been responsible for frequent failure of the metals therein. In addition, the prior method has been subject to the usual handicaps of batch processing, as contrasted to the efficient results obtained by continuous operation. It has also been proposed in the past to prepare solidified sodium-lead alloys by depositing on a rotating metal drum and solidifying thereon, followed by removal by a doctor blade to part the solidified alloy sheet from the drum. In extensive investigation of such a general technique, it has been discovered that the method is operable in quite a limited temperature range, particularly with respect to the adhesion of the alloy to the drum to the point of parting or delivery from the drum.

been found that the alloy tends to fall back over the drum into the supply of molten metal which is used to deposit a layer upon the drum.

An object of the present invention is to provide a process and apparatus suitable for the continuous manufacture of thin flakes of sodiumlead alloy. A more specific object is to provide a method and apparatus whereby the operation of a solidifying and comminuting apparatus is rendered less dependent of the final discharge temperature of the alloy. More particularly, an object of the invention is to provide an improved drum casting method and apparatus whereby delivery of virtually all alloy deposited on the drum to the discharge point is assured.

Broadly speaking, the invention comprises depositing a thin layer of molten sodium-lead alloy upon a metal drum having a plurality of peripheral bands consisting of the sodium-lead alloy being solidified. The above mentioned bands are relatively small sections of sodium-lead alloy already deposited in and solidified in inverted V-type grooves peripherally located on the drum surface. As such a band and the adjacent flat drum surface passes through the molten alloy bath provided for depositing alloy on the drum, the alloy partially liquefies the solid alloy in the above described bands and fuses thereto. As a result of this action, the solidified material on the drum thus resembles a thin sheet with intermittent bars projecting from the sheet surface to ward the center of the drum and actually keyed thereto by the retaining action of the inverted V-notch grooves. As the solidified alloy passes through the arc of the drum rotation, it is both solidified and sub-cooled sufiiciently to part the alloy from the metal of the drum surface. It has been found that as sodium-lead alloys solidify that the density increasesi. e., the alloy shrinks in size somewhat, thereby providing a mechanical force tending to part the alloy layer from the drum, in addition to the cessation of a binding force attributed solely to the results of the wetting efiect of molten alloy. As a. result of this partin action occasioned by the drop in specific volume of the solidified alloy, the alloy is then present as a series of relatively large, discrete flakes or small sheets, which are still retained by the action of the keyed-in bar sections cast within the drum grooves. Upon the point of discharge of the alloy product, a sharpened parting blade mounted adjacent to the drum surface and parallel to the axis thereof, sever-s the alloy sheet from the bar or root section imbedded in the drum grooves. This cutting action is accompanied by a relatively accentuated comminuting force and as a result the alloy particles will be discharged as moderately sized flakes.

The method of the improved process and-the details thereof will be more fully understood from the accompanying figures; Figure 1 being a schematic representation of the process and operation; Figure 2 being a partial sectional view of the section 2-2 of the drum surface, showing also a deposited portion of alloy prior to attainment of a sub-cooled temperature, and Figure 3 being a partial sectional view of'section 3-3 illustrating the relative disposition of the deposited alloy solids and a section of the drum at the point at which the alloy is suitable for parting or dis-l charge.

Referring to Figure l, the main item of the apparatus is a drum Hi having aplurality of pe ripheral grooves H in they outer surface. The grooves I l are characterized by being broader at the base thereof, that is, the grcoveopening is appreciably narrower than the root of the groove.

The drum in is rotated slightly immersed in a pool 12 of molten sodium-lead alloy. In passing through this pool, a thin layer i3 of alloy is deposited on the drum and solidified, heat being removed by a coolant supplied to the interior of the drum. Concurrently, the grooves l l are also filled with alloy which is similarly solidified. Alternatively, when the grooves are already filled with solid alloy uponrotation to the alloy supply pool, such alloy is; partly melted and bonded or fused with the, thin layer l3 deposited on the drum. This mode of action represents the normal operation. Continuing travel on the drum surface with its rotation, the solid alloy passes to a discharge, point, Where a parting knife or blade is parts the solidified thin alloy it from the drum Iii.

Parting knife 14 is'a sharpened blade, preferably of alloy steel, which bears lightly on the surface of the drum it. In preferred operation, the sole function ofthis blade is to sever the thin layer of alloy from the alloy ribs l5 which have been solidified in the grooves ll. Concurrently, in the preferred forms of the process, such thin particles are broken into relatively smaller portions [6 which are conducted by a chute it to a suitable hopper.

The drum ill and parting blade It are mounted within a suitable housing or shell, not shown, whereby an atmosphere of inert gas can be retained. This is a necessary and customary precaution in producing sodium-lead alloys, to prevent oxidation of the sodium content with atmospheric oxy en or moisture.

The details of operation are further illustrated. by Figure 2 and Figure 3, being sectional views of a portion of the drum wall with alloy deposited thereon, at different points in operation. Referring to Figure 2, the relative disposition of alloy and the drum wall is shown immediately after a layer l3 has been de osited, or, in fact while thealloy is still undergoing transitionto the, solid phase. It will be noted that the layer I3 and the alloy ribs [5 cast in the grooves l l form a unitary structure.

As the alloy configuration shown in Figure 2 is further cooled, appreciable shrinkage takes place. The relative disposition of the alloy and drum wall are then illustrated by Figure 3. Owing to the shrinkage encountered in the alloy upon freezing, the alloy in layer l5 tends to part fromthe drum surface by reason of the tendency to form anarcof smaller radius. Concurrently, asaresult of the shrinkage, in the alloy in the direction parallel to the axis of the drum, cracks 18 appear in the alloy section. Upon reaching h par ing b ade t s thus pos ble 9 em the thin layer l3 from the drum surface merely by severing the thin portion, or root, of the ribs 15 projecting from the alloy layer and wedged in the drum grooves H. A free space or slot 19 appearing between the alloy layer 13 and the drum surface facilitates this action, as it minimizes wearing of the parting blade I4.

The precise cross sectional appearance of the grooves in the drum is not of critical importance, the principal requisite being that the alloy ribs formed therein be narrower at the base (that is, at the, point of attachment to the layer of alloy) than at the top. Accordingly, although V-type grooves will customarily be used, other outlines are quite practical. For example, the groove may have one side at right angles to the drum surface and the other sideat an angle. A suitable groove has walls forming an angle of 30 to 45 to each other, being to of an inch wide at the drum surface, and approximately -inch deep.

With respect to the. spacing of the grooves axially on the drum, this spacing also can be varied with relatively Wide latitude. In virtually all instances, the spacing will be less than 3 inches, and preferably not less than about 1 inch. The precise spacing used is affected to a minor extent by the thickness of the alloy deposited. Thus, for an alloy layer of about inch mean thickness, a groove spacing of about 1 inch is preferred. For thicker alloy layers, the groove spacing can be increased. With the thicker section of the alloy layer, the mechanical strength is increased, andthe cracking or fractures resultant from cooling, as heretofore described, occur at less frequent intervals.

The parting blade of the apparatus is suitably mounted or supported by end bearings or trunnions which do not provide any lateral movement. In such instances the parting blade tends to wear more rapidly at the points at which the blade severs the alloy layer from the ribs. To provide more even wear and longer life, means may be provided to impart reciprocating motion to the blade during operation. Suitable devices for providing such motion are well known, for example, a. cam and follower operatively connected to the drum and the blade can provide such reciprocating motion. The latitude of such reciprocating motion should be at least equal to the spacing of the groovesin the drum.

As an illustrative but non-limiting example of the process and apparatus therefore, comparable to the embodiment of Figure 1, a steel drum, about 2 feet in diameter is provided. The drum surface is broken by peripheral grooves spaced at intervals of about 1 inch, the grooves being -inch wide at the drum surface and having walls equally diverging to provide a total angle of 30, the grooves being -inch deep.

A supply of molten monosodium lead alloy is maintained in contact with the lower portion of the drum, providing an immersion depth of about 3 inches. Heat removal is accomplished by circulating a stable oil Within the drum, to cool the alloy deposited on the drum to the freezing point of about 702 F. and then to sub-cool to a temperature of about 300 F. or lower.

In operation the drum is rotated. at a speed of 6 revolutions per minute. Alloy is deposited in the grooves and as a layer of about fl -inch thick. Upon reaching the parting blade, the layer of alloy is cracked into thin segments of irregular shape. The parting blade severs or fractures suchsegmentsfrom the ribs within the grooves. A production rate of about 40 pounds per minute is attained per foot of drum length. As previously described, a particular advantage .of the process is the fact that although the alloy can be sub-cooled below the freezing point sufiiciently to destroy the normal adhesion of the alloy to the drum surface, the temperature at which alloy loses adherence to the drum surface is somewhat variable. Factors which affect such temperature include the composition of the alloy and the degree of smoothness of the drum surface. As a normal matter, sub-cooling about 200 F. below the freezing temperature causes the alloy to lose adherence to the drum, but temperatures even below this level are preferred.

The process and apparatus described herein are of value in preparing sodium-lead alloys of widely varying composition. Of such alloys, the monosodium alloy is of greatest commercial importance, but the invention is not confined to a specific composition. Thus, alloys of higher sodium content, corresponding, for example, to NazPb, are also readily prepared. It will also be understood that sodium-lead alloys having minor concentrations of added catalyst components can be made by the process and are included in the term sodium-lead alloys.

Having described the invention and the best manner of operation, what is claimed is:

l. A drum caster for sodium-lead alloy comprising a drum having a plurality of parallel peripheral grooves in the drum, the grooves having walls diverging away from the drum surface, a parting knife bearing against with respect to the drum for parting a thin layer of alloy from said drum after solidification, a supply tank for molten sodium-lead alloy, the drum being rotatably mounted above said tank to be partially immersed in the said molten alloy within said tank supply for solidifying an alloy on the surface of said drum and in the grooves in the said drum, and a receiving surface for receiving the thin layer of solidified alloy after parting from the drum.

2. The apparatus of claim 1 further defined in that the walls of the peripheral grooves diverge at an angle of about 30 to 3. The process of casting a sodium-lead alloy comprising solidifying the alloy in the form of a thin layer on an endless casting surface, said surface having a plurality of parallel grooves, the grooves having walls diverging away from the casting surface, and having previously solidified alloy ribs substantially filling said grooves, said thin layer being fused to the said solidified ribs, the thin layer thereby being attached to the ribs at the narrowest point thereof, then severing the thin layer and the ribs adjacent the point of attachment to the thin layer and retaining the ribs in the grooves for further solidification of a thin alloy layer.

4. The process of casting a sodium-lead alloy comprising solidifying the alloy in the form of a thin layer on a rotating drum surface, said surface having a plurality of parallel peripheral grooves, the grooves having walls diverging away from the drum surface, and having previously solidified alloy ribs substantially filling said grooves, said thin layer being fused to the said solidified ribs, the thin layer thereby being attached to the ribs at the narrowest point thereof, then severing the thin layer and the ribs adjacent the point of attachment to the thin layer and retaining the ribs in the grooves for further solidification of a thin alloy layer.

GEORGE W. BESTE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 368,817 Daniels Aug. 23, 1887 510,808 Lloyd Dec. 12, 1893 2,074,812 Sendzimir Mar. 23, 1937 2,561,636 Pyk July 24, 1951 

1. A DRUM CASTER FOR SODIUM-LEAD ALLOY COMPRISING A DRUM HAVING A PLURALITY OF PARALLEL PERIPHERAL GROOVES IN THE DRUM, THE GROOVES HAVING WALLS DIVERGING AWAY FROM THE DRUM SURFACE, A PARTING KNIFE BEARING AGAINST WITH RESPECT TO THE DRUM FOR PARTING A THIN LAYER OF ALLOY FROM SAID DRUM AFTER SOLIDIFICATION, A SUPPLY TANK FOR MOLTEN SODIUM-LEAD ALLOY, THE DRUM BEING ROTATABLY MOUNTED ABOVE SAID TANK TO BE PARTIALLY 